Thermal switch with a bimetallic strip and a heat storage device

ABSTRACT

A thermal switch has a housing and a heat storage device having the shape of a parallelopipedic metal block swingably mounted by a pin in the housing. A bimetallic strip has an end fixed to the heat storage device on one side of its pin. A metal strip has an end fixed to the opposite side of the heat storage device. The metal strip carries electrical heating winding. A contact bridge is actuated by the bending of the bimetallic strip caused by the heating by the heat storage device.

United States Patent [72] Inventor Jakob Ellenberger Ernhoier Weg 2, Altdori, near Nuernberg, Germany [21] Appl. No, 874,255

[22] Filed Nov. 5, I969 [45] Patented Nov. 2, 1971 [32] Priority Nov. 7, 1968 [33] Germany [54] THERMAL SWITCH WITH A BIMETALLIC STRIP AND A IIEAT STORAGE DEVICE 8 Claims, 4 Drawing Figs.

[52] U.S. Cl 337/66, 337/81, 337/107 [51] Int. Cl H01h61/0l3, H01h 71/16, H0lh 73/30 [50] Field at Search 337/62, 66,

I 56 I References Cited UNITED STATES PATENTS 2,987,652 6/1961 Turnupseed 337/96 X 2,952,757 9/1960 Ellenberger 337/66 2,643,061 6/1953 Johnson 337/107 UX 2,311,801 2/1943 Winans.. 337/107 X 2,248,623 7/1941 Hand 337/82 Primary Examiner-Bernard A. Gilheany Assistant Examiner- Dewitt M. Morgan Atrorney Richards & Geier ABSTRACT: A thermal switch has a housing and a heat storage device having the shape of a parallelopipedic metal block swingably mounted by a pin in the housing A bimetallic strip has an end fixed to the heat storage device on one side of its pin. A metal strip has an end fixed to the opposite side of the heat storage device. The metal strip carries electrical heating winding. A contact bridge is actuated by the bending of the bimetallic strip caused by the heating by the heat storage device.

PATENTEU W2 19?! SHEET 1 BF 2 NOE INVIiN'ITJRD JAKOB ELLENBLRGER The invention relates to a thermal switch for an electrical circuit and more particularly to such a switch comprising a temperature-sensitive member and a switching member which is operated in dependence upon heating of the temperaturesensitive member by current. In known switches of this kind, the temperature-sensitive member generally consists of a bimetal strip, and very occasionally a heating wire. In switches provided with a bimetal strip, switching time lags from to 60 sec., while up to 90 sec. at most have hitherto been attained.

According to the present invention there is provided a thermal switch for an electrical circuit, such a switch comprising a temperature-sensitive member which is heatable in dependence of current flow, a switch member actuatable upon heating of the temperature-sensitive member and a heat storage device heatable in dependence of current flow and which alone is adapted to heat the temperature-sensitive member.

The switches of the invention may be constructed so that they have switching time lags in the range of I80 to 600 sec. at various excitation voltages, for example between 9 and 14 volts, and at different ambient temperatures, for example of -40 to +60 C. In addition, the switch may be constructed so that it is insensitive to shocks and accelerations, so that it may be employed more especially in automobiles, for example in a stationary vehicle heating system.

The heat storage device may be constructed as a metal block member, to one end of which there is secured the temperature-sensilive member constructed as a bimetal strip, and to the opposite end of which there is secured a metal strip provided with a heating winding through which current flows. When the currentflows through the heating winding, the latter first heats the metal strip and thereafter gradually heats the heat storage device, which finally heats the bimetal strip.

Like known switches, the present may be provided with a thermal trip and with a rockable locking pawl which, in its locking position, arrests the switching member in the circuitclosing position, and on heating of the bimetal strip releases the switching member. The locking pawl, which'may be constructed as a retaining lug, is secured to the free end ofa leaf spring which is clamped at one end and which bears with initial tension against the free end of the bimetal strip. In the cold state, the bimetal strip holds the leaf spring, against its initial tension, in a position in which it retaining lug holds fast the switching member in the circuit-closing position. When the bimetal strip is heated, it releases the leaf spring, so that the latter is so deflected owing to its initial tension that the retaining lug releases the switching member to enable it to move into the circuit-breaking position.

The heat storage device is rockably mounted substantially at its center or at its center ofgravity and the metal stiip provided with the heating winding is more or less tensioned. The greater the tension of its bimetallic strip the greater must be the amount of the current at which the circuit breaker is released. The length of the time delay is determined by the type and size of the heat storage device. The tripping current strength can be adjusted by setting the adjustment screw. A compression spring may also be provided which, in' the region of the adjustment screw acting as a traction screw, acts on that side of the metal strip which is further from the bimetal strip, the advantage is obtained that the play resulting from manufacturing tolerances is balanced out and the switch is rendered insensitive to shocks and accelerations or decelerations (impact of 50 G and acceleration of G).

For automatically balancing out excitation voltage differences, there is secured to the metal strip a current-heated bimetal strip lying in series with the heating winding, the free end of which bimetal strip is provided with a contact member which, when the bimetal strip is in the cold state, bears against a fixed contact member which is preferably adjustable by means of a screw. When the excitation voltage and thus also the excitation 'current are too high, this current heats the bimetal strip to such an extent that it deflects and lifts its movable contact member from the fixed contact member. The excitation current is thereby interrupted and only as much heat is supplied to the heat storage device as is necessary for producing the desired switching delay.

To compensate for the ambient temperature, there may be provided in parallel with the metal strip a compensating bimetal strip, which is connected to the free end of the metal strip. One end of the compensating bimetal strip may be introduced into a slot in the switch housing, while its other end may be pressed by a compression spring against an adjustable screw, while the compensating bimetal strip may be connected substantially at its center to the metal strip. Owing to the fact that the compensating bimetal strip is deflected in one direction or the other at its center, a corresponding turning of the metal strip provided with the heating winding, of the heat storage device and of the bimetal strip also takes place, so that corresponding deflections of this bimetal strip due to variation of the ambient temperature are balanced out.

Illustrative embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of one form of an open thermal switch in the circuit breaking position,

FIG. 2 is a similar view of the switch according to FIG. I in the circuit-closing position,

FIG. 3 is an elevational view of an open switch similar to that of FIGS. 1 and 2 with temperature compensation in the circuit-breaking position, and

FIG. 4 is a similar view of the switch according to FIG. 3 in the circuit-closing position.

The illustrated switches comprise a housing which consists of two halves of insulating material, only one housing half 1 being shown. The two housing halves may be connected together by hollow rivets extending through bores 2 in the housing halves. There are provided for the electrical connec tion, terminal connecting members 3 to 6 which may be constructed as flat plug pins and as such may be plugged into the corresponding sockets in a terminal board, whereby the switch is at the same time mechanically secured. The terminal connecting members 3 and 4 are associated with the main circuit which is to be broken by the switch, and the terminal connecting members 5, 6 are associated with theexcitation circuit. All the terminal connecting members 3 to 6 are adapted to be fitted into corresponding slots in the two housing halves.

The te'rminal'connecting member 3 has at its, upper end in accordance with FIG. I a fixed contact member 7 which cooperates with a contact member 8 oia contact bridge 9 constructed as a bellcrank lever. The terminal connecting member 4 is constiucted as an initially tensioned' leaf spring and has at its upper end in accordance with FIG. I a retaining lug '10 which extends over the left-hand end of the contact bridge 9 in the circuit-closing position as shown in FIG. 2 and thus retains this contact bridge 9 inthis circuit-closing position in which the contact member 8 of the contact bridge 9 bears against the fixed contact member 7 of the terminal con n'e cting merriber 3. g

Disposed between the two housing halves in a corresponding bore is a pushbutton 11 which is either rigidly connected to a switch rod 12 or formed integrally therewith. There acts on the push button 11 a circuit-breaking spring 13 which bears against an insulating disc 14 fitted in the two housing halves. Rigidly secured to the lower end of the switch rod l2 i s a switch bridge 15 consisting or a sheet metal section havii'ig on opposite sides projections 16 bent over at a right aiigi; and extending parallel to one another, which are guided in slots 17 the two housing halves. In this region, the contact bridge 9 pposi-te sides corresponding projections 18 which are guided in the same. slots 17. In the region ot the switch rod 12, the substantially horizontal arm l9 is formed with an aperture through which the switch rod 12 extends clearance in such manner that the contact bridge can slide a lially on the switch rod 12 and can rock on the projections 16 in the clockwise or counterclockwise direction in acalso has oh two 0 cordance with FIG. 1. A spring which effects the free tripping engages with clearance around the switch rod 12 and bears at one end against the arm 19 of the contact bridge 9 and at its other end against the switch bridge 15. The switch bridge 15 comprises a driving member 21 which cooperates with an abutment 22 on the contact bridge 9.

Disposed in a recess 23 in the housing, adjacent the terminal connecting member 4, is an insulating strip 24 which bears against that side ofthe terminal connecting member 4 which is further from the retaining lug 10. A bimetal strip 25 bears by means of a projection 26 at its free end against the insulated strip 24. The bimetal strip 25 is riveted at its other end to a heat storage device 27 consisting of a parallelepipedic metal block, for example constructed of copper-plated and nickelplated iron, and is rockably mounted on a pin 27' in the two housing halves. Riveted to that end of the heat storage device 27 which is opposite to the bimetal strip 25 is a metal strip 28 which supports an insulating sleeve 29 on which a heating winding 30 is coiled. The heating winding 30 is electrically connected at one end 31 to the metal strip 28 and at its other end 32 to the terminal connecting member 5. At its upper end according to FIG. I, the metal strip 28 is formed with a screw threaded hole into which an adjustment screw 33 is screwed, the head 34 of the latter being secured against axial displace ment in a corresponding recess 35 in the two housing halves. The adjustment screw 33 may be actuated by means of a screwdriver through a bore 36 in the two housing halves. The adjustment screw 33 serves to adjust the current at which the circuit breaker is released. A bimetal strip 37 is rigidly secured at its upper end according to FIG. I to the metal strip 28 below the adjustment screw 33. At this point, there acts on the bimetal strip 37 or on the metal strip 28 a compression spring 38 which bears against the base of a corresponding recess in the two housing halves. The free end of the bimetal strip 37 is provided with a contact member 39 which bears against a contact member 40 on the terminal connecting member 6 when the bimetal strip 37 is cold. The contact member 40 may be adjusted by means ofa screw 41 from the outside with the aid of a screwdriver. A nut 42 into which the screw 41 is screwed is fitted into a corresponding aperture in the housing in such manner as to be axially nondisplaceable.

In accordance with FIGS. 3 and 4, there is mounted in a slot 43 in the two housing halves a compensating bimetal strip 44, on one side of the upper end of which there acts a compression spring 45, while there acts on the other side thereof a screw 46 screwed into a nut 47. The nut 47 is situated in a corresponding recess 48 in the two housing halves. The metal strip 28 is provided with a transverse portion 49 by which it bears against the compensating bimetal strip 44 under the ac tion of the compression spring 38. In the region of the compensating bimetal strip 44, the opposite walls of the two housing halves are formed with apertures 50 through which the external temperature can influence the compensating bimetal strip 44. The screw 46 can be actuated by means of a screwdriver through a bore 51 extending through the two housing halves.

As already stated, when the bimetal strip 44 is bent by the surrounding temperature over the part 49, the metal strip 28 and the heat storage device 27, the bimetal strip 25 is so swung that its projection 26 will always remain in position shown in FIG. 4. This means that when, for example, the bimetal strip 25 is bent to the left (FIG. 4) due to an increase in surrounding temperature then the compensating bimetal strip 44 is moved td the right in the range of the portion 49. The compression spring 38 presses the metal strip 28 with its portion 49 against the bimetal strip 44, whereby the metal strip 28 and the heat storage device 27 rigidly connected therewith swing clockwise. The bimetal strip 25 rigidly connected with the heat storage device 27 also participates in this movement thereby balancing the bending of the bimetal strip 25.

The two switches operate as follows:

It will be assumed that the two switches are in the circuitclosing position according to FIGS. 2 and 4, which is indicated by the pushbutton 11 being in its depressed position. The current to be interrupted flows from the terminal connecting member 3 through the contact members 7, B, the contact bridge 9 and the retaining lug 10 acting as a contact member to the terminal connecting member 4, while the excitation current flows from the terminal connecting member 5 through the heating winding 30, the upper part of the metal strip 28, the bimetal strip 37 and the contact members 39, 40 to the terminal connecting member 6. The insulating strip 24 electrically isolates the excitation circuit from the main circuit to be interrupted. The excitation current heats the heating winding 30, which heats the metal strip 28. The metal strip 28 in turn heats the heat storage device 27, which heats the bimetal strip 25. The bimetal strip 25 is deflected to the left in accordance with FIGS. 2 and 4, whereby its projection 26 releases the insulating strip 24 and the terminal connecting member 4 constructed as an initially tensioned contact spring, so that the latter is enabled to deflect to the left in accordance with FIGS. 2 and 4. When the terminal connecting member 4 has been sufficiently deflected, its retaining lug l0 releases the contact bridge 9, so that the latter is brought under the action of the circuit-breaking spring 13 and of the spring 20 into engagement with an inclined surface 52 of the two housing halves. This circuit breaking position is indicated by the pushbutton 11 projecting out of the switch housing. When the pushbutton 11 is held fast in the depressed position during this tripping action, so that the circuit-breaking spring 13 cannot operate, a tripping, i.e. the so-called free trip, takes place under the action of the spring 20.

When the bimetal strip 25 has cooled sufficiently, its projection 26 presses against the insulating strip 24, which in turn presses against the terminal connecting member 4 until, when the bimetal strip 25 has completely cooled, the terminal connecting member 4 is situated with its retaining lug 10 in the position illustrated in FIGS. 2 and 4. When the pushbutton 11 is then pushed into the switch housing, the driving member 21 of the switch bridge 15 engages the contact bridge by means of its abutment 22 and drives the latter into the circuit-closing position. The retaining lug 10 with the terminal connecting member 4 and the bimetal strip 25 is thus resiliently pushed away to the left as seen in the figures by the contact bridge 9, whereafter the retaining lug 10 engages over the left-hand end of the arm 19 of the contact bridge 9. When the push member 11 is released, the contact bridge 9 rocks about the retaining lug l0, acting as a pivot, in the counterclockwise direction. As soon as the abutment 22 of the contact bridge slides off the driving member 21, the contact bridge 9 is suddenly further rocked in the counterclockwise direction by the tensioned spring 20 and its contact member 8 is brought into engagement with the fixed contact member 7 of the terminal connecting member 3. This sudden circuit closing constitutes an instantaneous circuit closing. The illustrated switches thus have an instantaneous circuit-closing action and an instantaneous circuit-breaking action, whereby the wear on their contact members is minimized and their useful length is increased.

If the excitation voltage present at the terminal connecting members 5, 6 is high, the bimetal strip 37 is so heated that its contact member 39 is lifted from the fixed contact member 40 (chain-lined position in FIGS. 1 and 3), whereby the excitation circuit, and thus the heating of the metal strip 28 and of the heat storage device 27 and hence of the bimetal strip 25, is interrupted. As soon as the bimetal strip 37 has cooled somewhat, its contact member 39 again bears against the contact member 40, whereby the heating is continued. Thus, for the regulation of the heating, the contact member 39 of the bimetal strip 37 is repeatedly lifted from the contact member 40 and applied against it during operation. The higher the excitation voltage, the higher is the number of interruptions of the heating in a particular time. This ensures that the heatingup and thus the time lag in the switching remain constant with different excitation voltages. The excitation energy may be adjusted by adjustment of the screw 41.

Switching time lags of appropriate length can be obtained in accordance with the size and the construction of the heat storage device 27. Such long delays in circuit breaking are required in automobile vehicles, especially in town journeys, when the petrol heating (consumption about 0.3 liters per hour) often starts owing to the stopping times at trafiic lights. The preheating taking place each time there is a stop has a cumulative effect, so that when the disconnection takes place before 3 minutes disconnections occur which are technically unnecessary and which in practice have a disturbing efiect.

Ribs 53 on the two housing halves surround the compensating bimetal strip 44 and prevent heat from being transmitted to the bimetal strip 25 and to the compensating bimetal strip 44 by radiation from the heating winding 30.

Iclairn:

l. A thermal switch, comprising a housing, a heat storage device having the shape of a parallelopipedic metal block, a pin swingably supporting said heat storage device within said housing, a bimetal strip having an end fixed to said heat storage device to one side of said pin, a metal strip having an end fixed to said heat storage device to the opposite side of said pin, an electrical heating winding carried by said metal strip, a contact bridge, and means actuated by the bending of the bimetal strip when the bimetal strip is heated by said heat storage device for actuating said contact bridge.

2. A switch according to claim I, wherein said means comprise a leaf spring located within said housing and having an end fixed to said housing, said leaf spring having another free end bearing against the free end of said bimetal strip and a retaining lug carried by the free end of said leaf spring, said retaining lug being adapted to engage said contact bridge and hold it in a closed position when the bimetal strip is bent.

3. A switch according to claim 1, further comprising an adjustable screw carried by said housing and engaging the opposite end of said metal strip, said pin supporting said heat storage device substantially in its center.

4. A switch according to claim 3, further comprising a compression spring carried by said housing and engaging that surface of said opposite end of said metal strip which is furthest from said bimetal strip.

5. A switch according to claim 1, comprising a second bimetal strip having an end connected to the other end of said metal strip and connected in series with said electrical heating winding, a contact carried by the other end of said second bimetal strip, a second contact and means carried by said housing and carrying said second contact, said second contact engaging the first-mentioned contact when said second bimetal strip is cold.

6. A switch according to claim 5, wherein the last-mentioned means consist of a screw adapted to adjust the position of said second contact.

7. A switch according to claim 1, comprising a compensating bimetal strip connected to the other end of said metal strip for the compensation for ambient temperature.

8. A switch according to claim 7, comprising a compression spring and an adjustable screw, one end of said compensating bimetal strip being located in a slot formed in said housing, said compression spring being connected with said adjustable screw and the other end of said compensating bimetal strip, said metal strip being connected substantially to the center of said compensating bimetal strip.

i i k 

1. A thermal switch, comprising a housing, a heat storage device having the shape of a parallelopipedic metal block, a pin swingably supporting said heat storage device within said housing, a bimetal strip having an end fixed to said heat storage device to one side of said pin, a metal strip having an end fixed to said heat storage device to the opposite side of said pin, an electrical heating winding carried by said metal strip, a contact bridge, and means actuated by the bending of the bimetal strip when the bimetal strip is heated by said heat storage device for actuating said contact bridge.
 2. A switch according to claim 1, wherein said means comprise a leaf spring located within said housing and having an end fixed to said housing, said leaf spring having another free end bearing against the free end of said bimetal strip and a retaining lug carried by the free end of said leaf spring, said retaining lug being adapted to engage said contact bridge and hold it in a closed position when the bimetal strip is bent.
 3. A switch according to claim 1, further comprising an adjustable screw carried by said housing and engaging the opposite end of said metal strip, said pin supporting said heat storage device substantially in its center.
 4. A switch according to claim 3, further comprising a compression spring carried by said housing and engaging that surface of said opposite end of said metal strip which is furthest from said bimetal strip.
 5. A switch according to claim 1, comprising a second bimetal strip having an end connected to the other end of said metal strip and connected in series with said electrical heating winding, a contact carried by the other end of said second bimetal strip, a second contact and means carried by said housing and carrying said second contact, said second contact engaging the first-mentioned contact when said second bimetal strip is cold.
 6. A switch according to claim 5, wherein the last-mentioned means consist of a screw adapted to adjust the position of said second contact.
 7. A switch according to claim 1, comprising a compensating bimetal strip connected to the other end of said metal strip for the compensation for ambient temperature.
 8. A switch according to claim 7, comprising a compression spring and an adjustable screw, one end of said compensating bimetal strip being located in a slot formed in said housing, said compression spring being connected with said adjustable screw and the other end of said compensating bimetal strip, said metal strip being connected substantially to the center of said compensating bimetal strip. 